# Tag Info

11

Because the frequency of a sound wave is defined as "the number of waves per second." If you had a sound source emitting, say, 200 waves per second, and your ear (inside a different medium) received only 150 waves per second, the remaining waves 50 waves per second would have to pile up somewhere — presumably, at the interface between the two media. ...

10

When you pluck a string or hit a drum or sound a not on a flute, the instrument and the air in and around it vibrate and this vibration propagates as sound waves in the air to your hear drum. When you hear an instrument being played, what you recognise as the note is the base frequency. 'C' corresponds to $261.6$ Hz and is the same for a piano or a guitar. ...

8

This has to do with continuity of the wave motion. Imagine you had a change in frequency going from medium A to medium B - say 10 Hz become 20 Hz. How do you make something move at 20 Hz? You need to apply a driving force at 20 Hz of course. But the incoming wave is going at 10 Hz. To add energy to the wave we must be pushing when it it moving away from us ...

7

Update with a more clear answer: Here's a plot of all the velocities involved with shock propagation through a sationary medium: The x axis is the mach number of the shock wave and represents the strength of the shock wave, it could have been velocity or pressure ratio or any other quantity that is monotonic with shock strength. The y-axis is velocity ...

4

Speed of sound in water at 20 degrees Celsius is 1482 m/s., (2881 knots), just for comparison to current claimed achievable speeds. Small related fact: The pistol shrimp can create sonoluminescent cavitation bubbles that reach up to 5,000 K (4,700 °C) which are as loud as 218 decibels, breaking the sound barrier in water. Says Wikipedia YouTube video of ...

4

The reason that the speed of sound is a well-defined quantity is that, for small pertubations, the equations which govern the fluid dynamics can be linearised. In that linearised form, the solution boils down to a simple wave ansatz with linear dispersion relation, i.e. constant velocity.Those are the sound waves. It so happens that in air, this linear ...

4

Occam suggests that the sounds are either able to be explained as typical noises that 'just happen' or are hoaxes. It is unfortunately extremely common for a large number of copy-cat reports of major "strangenesses" to occur once something suitably notable appears "on the web". There are numerous web discussions about these "phenomena". This 14 minute ...

3

Pitch, in music, is equivalent to frequency. How often the wavefore cycles. This is usually defined by length, i.e. how long the string is, how long the pipe is, etc. It can also be affected by the tension (how tight the string is.) Timbre, the sound of a specific instrument, is defined by the "shape" of the wavefore, whether spikes, round, square, or ...

2

Frequency, in physics, is the number of crests that pass a fixed point in the medium in unit time. So it should depend on the source not on the medium. If I take a source who vibrates faster than yours then number of crests that my source can create per second (for example) will be more than yours. But speed of the wave depend on the properties of the ...

2

You hear the boom when you and the cone overlap. It doesn't matter whether you move "into" the cone, or "out of" it - there will be a sharp transition in pressure. Maybe plane B hears a "moob cinos". It will still be loud.

2

Let me say what others are trying to say, hopefully in a clearer fashion: Just because you can relate two variables in an equation does not mean that they are dependant. In this case, you have to constrain intensity $I$ in order to get the relationship. At that point, it is not a general relationship, but only true when $I$ is constrained. An example that ...

2

The speed of mechanical sound waves through the air at 0 degrees C is 331 m/sec. But sound can travel at many different speeds, depending on the medium it propagates through and the temperature and pressure, among other variables. What we call sound is any mechanical wave within the range of human perception that is transmitted to our eardrums via the air. ...

2

The question could be rephrased as, is it possible to create an analogue of an "image" of a three dimensional object acoustically? The answer to this question is clearly yes, provided that the wavelength of the sound used to do the imaging is sufficiently small compared to the object being imaged. One example is in the energy industry - geophysicists use ...

1

The answer is: not much. The usual analogy is waves at the beach. You can see a long line of waves rolling towards the land, but the water never actually moves across the land. Waves, whether water or sound, transmit energy by passing it along from one particle to the next. The medium itself oscillates but doesn't really go anywhere. There are ...

1

The maximum change of pressure caused by a sound wave is its pressure amplitude. This would be the difference between high and low pressure areas in the sound wave. When sound is measured in pascals, however, for the purpose of computing decibels by comparing with other sounds, it's just the high pressure against the measuring surface, to the extent that ...

1

Yes this is related to Stoke's law for sound attenuation, which states that a plane wave decreases amplitude exponentially with a factor $\alpha$ given by: $$\alpha = \frac{2\eta\omega^2}{3\rho V^3}$$ where you can see that the dependence on the frequency squared $\omega$ of the sound will yield a higher coefficient of attenuation for higher frequency ...

1

Sound waves in air are a series of high and low pressure areas moving through the elastic medium of the air. If the medium is being compressed and rarefied by other areas of high and low pressure, the integrity of the sound wave may be broken and may become unrecognizable through the background noise of the medium's turbulence. Here is an explanation of ...

1

The process of auditory masking can partially answer the question. A constant wind can present fairly high intensity middle and high frequency noise (pink noise) to the ear. This will mask these frequencies in the speaking voice. These frequencies (>1 kHz) are generally responsible for the "diction" of speech, so you may be able to tell that someone is ...

1

There isn't a simple formula for fan noise, but the physics can be worked out from the fundamental equations of fluid mechanics and acoustics. It isn't a simple problem however. The noise created by fans is complex and from several fundamental sources, and its amplitude depends on frequency. Here is an example of a fan noise frequency spectrum for a cooling ...

1

The speed of sound in an ideal gas is given by: $$v = \sqrt{\gamma\frac{P}{\rho}}$$ where $P$ is the pressure, $\rho$ is the density and $\gamma$ is the heat capacity ratio. For ideal diatomic gases $\gamma = 1.4$. In fact for air at 20ºC $\gamma$ is almost exactly 1.4, while for hydrogen it's 1.41, so pretty close to ideal behaviour.

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